Turbulent Mixing in Stratified Flows

The world’s oceans, lakes and atmospheres and many astrophysical bodies are stably stratified, in that the density of the fluid increases in the direction of the gravitational force. A fluid particle displaced from its equilibrium position is then subject to a restoring buoyancy force that tends to return it to its equilibrium position. On Earth, this means that vertical motions are inhibited by the stratification, providing an impediment to vertical exchanges of mass. However, these vertical exchanges and any consequent mixing are critical determinants of the structure of these natural fluid bodies. For example, the uptake of heat and carbon dioxide into the ocean from the surface depends critically on how these quantities are mixed down into the ocean interior, an essential aspect of the climate system. This mixing is caused predominantly by turbulent motions generated by shear flows, breaking internal waves and other forcing mechanisms interacting with large scale motions.
Over the past ten years or so there have been major advances in our understanding of stratified turbulence. This has been largely brought about by improved computational capabilities that allow direct numerical and large eddy simulations of stratified flows, coupled with significantly improved experimental diagnostics. In addition field measurements have provided new data at geophysical scales that have caused a re- evaluation of the extrapolations of data from numerical and laboratory studies. There has also been significant progress in understanding transitions from stratified laminar to turbulent flows through the application of modal as well as non-modal analysis.
This course brings together six leading researchers specializing in stratified turbulence and mixing to teach focused and highly original courses in this area. They will present the latest findings from stability theory on the laminar to turbulent transition, and discuss the recent progress in scaling stratified turbulent flows. The latest laboratory experiments will be presented and the impact of new highly-resolved three dimensional fields of velocity and density and the relation to the latest numerical simulations. Important quantities such as mixing efficiency and the relation to the underlying non- dimensional parameters and the molecular properties of the fluid involved will be highlighted. Lectures will also cover the role of stratified turbulence in the oceans, atmosphere and in astrophysics.
Learning skills in this interdisciplinary environment is challenging and rarely addressed to a sufficient level in standard graduate programs. The integrated presentation of theoretical, experimental and numerical research coupled with applications in geophysical and astrophysical fluid dynamics, provides a valuable opportunity to learn about this important field of fluid dynamics. The course is intended for doctoral and postdoctoral scholars in physics, applied mathematics, engineering, oceanography and meteorology.